Generally, PC cards, such as memory cards, are data input devices which are electrically connected to an electronic apparatus or storage device, such as a word processor, personal computer or other electronic apparatus. The data stored in the PC card is transferred to the electronic apparatus. Memory cards are portable instruments which are readily inserted and extracted from a connector apparatus which may be used with the PC card for removably coupling the PC card to a printed circuit board, for instance.
A PC card conventionally includes a frame which usually is generally rectangular and includes an opening in either a top surface or a bottom surface thereof or, in some constructions, in both surfaces. The opening receives a circuit board assembly, and a panel or cover closes the opening and encloses the circuit board assembly within the frame. Often, a pair of panels or covers sandwich the frame and the circuit board assembly therebetween.
The circuit board assembly of a PC card conventionally includes a generally planar dielectric substrate with circuit traces and at least one electrical component mounted thereon. The electrical component(s) may include semi-conductor devices, integrated circuits, batteries or the like.
One of the problems associated with PC cards involves the build-up of electrical charges in the PC card. Specifically, charges are generated in the PC card during handling since the card generally is a portable instrument often carried on a human body. When a card bearing charges is inserted into an electronic apparatus or the connector thereof, the charges flow to the electronic apparatus through the connecting terminals of the connector. The charges can result in damage to or ultimate failure of the integrated circuits or other circuit elements on the card as well as the electronic apparatus itself.
Consequently, a typical PC card is shielded by making the panels or cover conductive to protect the electrical circuitry, and in particular, the electromagnetic signals, from externally generated radiated emissions. The card is also provided with EMI or grounding contacts along outside edges thereof to provide early discharge of internally generally static electricity in order to minimize the effects of electromagnetic pulses created during the dissipation of static charges through the signal contacts. Typically (according to such standards as PCMCIA), two grounding locations are established on the outside edges of the PC card with corresponding grounding contacts inside the guide arms of a card-receiving header connector. However, this standard grounding configuration is only intended for reduction of ESD and EMI/RFI effects, and does not address the effects of signal distortion. That is to say, in a given electrical circuit with given inductance and resistance values, the current flowing through the signal terminals must be balanced with the current flowing through the ground returns. If this balance is not achieved, voltage build-up can occur on the ground, or reference conductors, thus distorting the electrical signals and creating "ground bounce". Furthermore, at high switching speeds, the existing ground pins in the header are often insufficient, and if the grounding locations connected to the grounding contacts inside the guide arms are also connected to the ground pins within the header, it may cause a current to flow from the ground pins through the conductive cover and to the guide grounds thus creating a "ground loop".
One method of adding ground paths in parallel to decrease voltage build-up and minimize the occurrence of ground bounce is disclosed in U.S. Pat. No. 5,288,247 to Kaufman, dated Feb. 22, 1994. In that design, a grounding shroud is placed around a card-receiving header connector which shroud includes a plurality of contacts which engage a portion of a PC card shell and balances the ground returns with the current flow of the system.
However, the approach disclosed in the '247 patent does not solve the problem of ground loops and actually can contribute further to grounding and shielding complications. Since the ground loop flowing through the cover may create radiation and result in an antenna-like effect instead of providing a shielding function, thus further comprising the grounding function of the card.
The present invention is directed to solving the problems discussed above and providing an improved grounding system in a connector assembly for a PC card.